Re: [PATCH v6 01/12] mm/sparsemem: Introduce struct mem_section_usage

[Pavel Tatashin]

On Thu, May 2, 2019 at 2:07 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> On Wed, May 1, 2019 at 4:25 PM Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:
> >
> > On 19-04-17 11:39:00, Dan Williams wrote:
> > > Towards enabling memory hotplug to track partial population of a
> > > section, introduce 'struct mem_section_usage'.
> > >
> > > A pointer to a 'struct mem_section_usage' instance replaces the existing
> > > pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
> > > 'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
> > > house a new 'map_active' bitmap.  The new bitmap enables the memory
> > > hot{plug,remove} implementation to act on incremental sub-divisions of a
> > > section.
> > >
> > > The primary motivation for this functionality is to support platforms
> > > that mix "System RAM" and "Persistent Memory" within a single section,
> > > or multiple PMEM ranges with different mapping lifetimes within a single
> > > section. The section restriction for hotplug has caused an ongoing saga
> > > of hacks and bugs for devm_memremap_pages() users.
> > >
> > > Beyond the fixups to teach existing paths how to retrieve the 'usemap'
> > > from a section, and updates to usemap allocation path, there are no
> > > expected behavior changes.
> > >
> > > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > > Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> > > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>